A magnetic conductor corresponds to a general electric conductor. A tangential component of an electric field is almost ‘0’ on a surface of an electric conductor, while a tangential component of a magnetic field is almost ‘0’ on a surface of a magnetic conductor. Thus, a current does not flow on the surface of a magnetic conductor differently from that of an electric conductor.
A magnetic conductor operates as a component which has a considerably high resistance in a specific frequency, i.e., performs a function of an open circuit, due to the characteristic of the magnetic conductor. A specific unit cell patterns may be periodically arrayed on the general electric conductor to realize the magnetic conductor. The magnetic conductor is referred to as an artificial magnetic conductor (AMC).
A surface of the AMC has a high impedance surface (HIS) characteristic in terms of the circuit as described above. The HIS characteristic depends on a specific frequency according to formed AMC patterns.
An antenna generally requires a distance of ¼ or more of a wavelength λ of a transmitted and received signal from a ground surface of the electric conductor. If the antenna is at a closer distance than λ/4, a surface current flowing in an opposite direction to a current flowing in the antenna is inducted to the ground surface of the electric conductor. Thus, the two currents are offset. As a result, the antenna cannot operate effectively. However, since a current does not flow on a surface of the AMC, the antenna operates much closer to the AMC than the electric conductor. As a result, a distance between the ground surface of the electric conductor and the antenna can be reduced.
Interest in tags mountable on conductors and tags usable on high dielectric materials such as water has increased in the field of the development of tag antennas of wireless identification systems such as radio frequency identification (RFID). General tag antennas that are mounted on conductors cannot operate as antennas. However, tag antennas using AMCs can be mounted on vehicles, container boxes, or the like to be sufficiently utilized, thus expanding the utilization of wireless identification systems.
FIGS. 1A and 1B are side and perspective views, respectively, of an AMC 10 applied to a conventional antenna.
Referring to FIG. 1A, the AMC 10 includes a ground layer 18, a first dielectric layer 14, an AMC layer 12, and a frequency selective surface (FSS) layer 22.
The AMC layer 12 is connected to the ground layer 18 through vias 16 formed of metal, and the FSS layer 22 is connected to the ground layer 26 and a power source to form a capacitor 24.
Referring to FIG. 1B, patterns of the AMC layer 12 are arrayed in simple square patches. The simple square patches are electrically connected to the ground layer 18 through the vias 16 formed of metal. A monopole type antenna (not shown) is mounted on the AMC layer 12, and the FSS layer 22 is capacitively loaded in order to reduce a length of the antenna.
The first dielectric layer 14 is formed at a distance of about 1/50 of a wavelength λ of a transmitted and received signal from the ground layer 18. A conventional antenna does not need a distance of ¼ or more of a wavelength of a transmitted and received signal from a ground layer due to an AMC.
A conventional antenna using an AMC as illustrated in FIGS. 1A and 1B includes vias for the AMC. Also, an antenna such as a monopole antenna is mounted on the AMC. The monopole antenna is supplied with power from a feeding port to operate. Accordingly, since a conventional antenna necessarily includes vias, the formation of an AMC is complicated. Also, since a conventional antenna includes a feeding port for supplying power, a structure of the conventional antenna is complicated, and the size of the conventional antenna is increased.